Neisseria meningitidis, a Gram-negative bacterium, is a major human pathogen that causes bacterial meningitis and sepsis. The attack and morbidity rates are highest in children under 2 years of age. Five major capsular groups account for nearly all disease-producing isolates. These are defined by different polysaccharide capsules designated A, B, C, Y and W-135. Vaccines are available for prevention of disease caused by group A, C, Y and W-135 organisms. However, there is no vaccine available for prevention of disease caused by group B strains (hereafter referred to as “NmB”), which account for 50 percent or more of all cases of meningococcal disease in children in the US and Europe (Jones, D., in “Meningococcal Disease,” John Wiley & Sons, New York, 1995).
The meningococcal group B capsular polysaccharide (referred to herein as NmB capsular polysaccharide or “NmB PS”) is composed of a homolinear polymer of alpha2→8) N-acetyl neuraminic acid (polysialic acid; hereafter referred to as “PSA”). This capsular PS is conserved across all NmB strains, and is also found in pathogenic Escherichia coli K1. NmB PS is chemically identical to polysialic acid that is abundantly expressed by fetal tissues, including brain, heart, and kidney.
The Group B capsule is an important virulence determinant. For example, mutants that are deficient in capsular expression are serum-sensitive and non-pathogenic (Stephens 1991, Infect Immun 59:4097). Evidence also indicates that serum antibody to the group B polysaccharide confers protection against disease by activating complement-mediated bacteriolysis and/or opsonization (Griffiss, J. M., in “Meningococcal Disease,” John Wiley & Sons, New York, 1995).
However, efforts to employ the NmB capsular polysaccharide as a vaccine component have been hampered by its poor immunogenicity (Wyle et al., 1972, J. Infect. Dis. 126: 514-522; Zollinger, et al., 1979, J. Clin. Invest. 63: 836-834), even when conjugated to a carrier protein (Devi et al., 1997, Infect Immun 65:1045; Jennings et al., 1981, J Immunol 127:1011). The poor immunogenicity is attributed to immunologic tolerance induced by fetal exposure to cross-reactive polysialated glycoproteins expressed in a variety of host tissues such as the neural cell adhesion molecule (“NCAM”) (Finne et al. 1983, Biochem Biophys Res Commun 112:482; Hayrinen et al. 1995, J Infect Dis 171:1481). Anti-NmB PS monoclonal antibodies (mAbs) have been prepared by immunizing mice with killed group B bacteria (Mandrell et al. 1982 J Immunol 129:2172; Moreno et al. 1983 J Gen Microbiol 129 (Pt 8):2451; Shin et al. 2001 Infect Immun 69:3335), or by immunizing NZB mice with plain polysaccharide or bacteria (Frosch et al. 1985 Proc Natl Acad Sci USA 82:1194; Hurpin et al. 1992 Hybridoma 11:677). Human NmB PS-reactive IgM mAbs or paraproteins have also been described (Raff et al. 1988 J Infect Dis 157:118; Rohr et al. 1980 J Biol Chem 255:2332; Azmi et al. 1994 Infect Immun 62:1776; Mandrell et al. 1995 J Infect Dis 172:1279). These mAbs or paraproteins elicit complement-mediated bactericidal activity. Thus development of vaccines based on polysaccharide as an antigen, but with improved immunogenicity, has been a particular focus in the field.
In the 1980s, Jennings and coworkers investigated the immunogenicity of various derivatives of NmB PS (Jennings et al., 1981, supra Jennings 1985 J Immunol 134:2651; Ashton et al. 1989 Microb Pathog 6:455; Pon et al. 1997 J Exp Med 185:1929). Conjugate vaccines containing polysaccharides in which N-acetyl groups of NmB PS were replaced with a variety of more hydrophobic acyl groups, particularly propionyl (N-Pr), were immunogenic and elicited protective bactericidal antibody. The resulting modified polysaccharide was conjugated to a protein carrier (Jennings et al. 1986, J Immunol 137:1708, 1986; Jennings et al. 1987, J Exp Med 165:1207; Jennings et al., 1981, supra; Jennings et al. 1985 supra; Asthon et al. 1989, supra; Pon et al. 1997, supra; U.S. Pat. No. 4,727,136) and found to be immunogenic in experimental animals, eliciting IgG antibodies that activated complement-mediated bacteriolysis in vitro, and conferring passive protection in experimental animals infected with NmB. This vaccine was immunogenic in sub-human primates, inducing serum antibodies that activate complement-mediated bacteriolysis (Fusco et al., 1997, J. Infect. Dis. 175: 364-372). In humans, bactericidal antibodies are known to confer protection against developing meningococcal disease (Goldschneider et al.,. 1969, J. Exp. Med. 129:1307).
However, a subset of the antibodies induced by the currently available vaccines has anti-host autoantibody activity to unmodified NmB PS (i.e. N-acetyl-NmB PS) (Hayrinen et al. 1995 J Infect Dis 171:1481; Granoff et al., 1998, J. Immunol; 160: 5028-5036). Since PSA is abundantly expressed in fetal and newborn tissue, especially on NCAMs found in brain tissue, this approach raises serious safety concerns. Remarkably, a subset of bactericidal antibodies elicited by N-Pr and other derivatives of NmB PS bound specifically with bacteria and not with host tissues, and were not absorbed by NmB PS affinity matrices (Jennings et al. 1989 J Immunol 142:3585; Pon et al. 1997, supra). Granoff et al. immunized mice with N-Pr NmB PS conjugated to tetanus toxoid and prepared a panel of monoclonal anti-N-Pr NmB PS antibodies (mAbs) (Granoff et al. 1998 J Immunol 160:5028). A number of the mAbs elicited complement-mediated bactericidal activity in vitro, and conferred passive protection against bacteremia in an infant rat model. The protective mAbs were subclassified into four different fine antigenic specificity groups based on the presence or absence of cross-reactivity with native NmB PS, and the ability of N-Pr-MB oligosaccharides (average degree of polymerization [Dp]=3.8) to inhibit anti-N-Pr-NmB PS binding in an ELISA. MAbs, representative of each of the four fine antigenic specificity groups, showed minimal or no detectable autoreactivity with the host polysialic acid based on flow cytometry studies with the human cell line CHP-134 (Granoff et al. 1998, supra), which express long chain polysialic acid, and immunohistology with human fetal tissue. The mAbs bound to the surface of live encapsulated group B bacteria but riot to a capsular deficient mutant. The epitopes on the bacteria recognized by these anti-N-Pr NmB PS mAbs were not defined.
The present invention overcomes the disadvantages of prior art approaches to vaccination by providing vaccine compositions and methods that elicit an immune response, particularly a protective immune response, against Neisseria meningitidis Group B strains, while at the same time eliciting no detectable or significant auto-antibodies against host tissues.
Literature
PCT Publication No. WO99/10372 (anti-N-Pr NmB PS mAbs, claiming priority to U.S. provisional application Ser. No. 60/058,001, filed Aug. 27, 1997); U.S. Pat. No. 6,048,527 (anti-NmB antibodies); U.S. Pat. No. 6,350,449 (anti-NmB antibodies).
U.S. Pat. No. 6,030,619 (Granoff and Moe (mimetics))
U.S. Pat. No. 4,727,136 (Jennings (N-Pr NmB PS vaccine))
U.S. Pat. No. 6,638,513;
Fusco et al. “Preclinical evaluation of a novel group B meningococcal conjugate vaccine that elicits bactericidal activity in both mice and nonhuman primates,” (1997) J. Infect. Dis. 175:364-72.